Over the last century, humans have littered the oceans with plastic, pumped CO2 into the air and raked fertilisers across the land. The impact of our species is so severe and so enduring that the current geological time period could soon be declared the “Anthropocene”.

This was the recommendation of a group of scientists in August. The announcement was the product of years of work and, arguably, arrived on the shoulders of centuries of scientific and philosophical grappling with the idea of humanity’s role in shaping the world.

Even so, the Anthropocene is far from becoming a formal piece of the geological jigsaw. While the idea has been seized enthusiastically by many in the fields of science and beyond, there are some who question the validity of naming a new epoch after humanity.

History

Antonio Stoppani is often cited as the first person to suggest that the current geological epoch should be defined by the influence of humans. Formerly a Catholic priest, the Italian professor had turned to geology after he was expelled from the seminary where he taught grammar for his political fervour.

Stoppani saw the footprints of humanity everywhere: it had carved the paths of rivers, mined the Alps, dammed the ocean and built cities. “The Anthropozoic era has begun: geologists cannot predict its end at all,” he wrote in his 1873 work Corso di Geologia. And while the so-called Anthropozoic era might have only lasted a “handful of centuries” so far, he predicted that our species’ influence would continue long into the future.

His ideas may have been influenced by American conservationist George Perkins Marsh, who was ambassador to Italy at the time, although Marsh himself acknowledges that Stoppani went further than he ever did.

Throughout the 19th and 20th centuries, more geologists played with the idea of introducing humanity into the sequence of geological time periods.

Joseph Le Conte, American geologist and co-founder of the Sierra Club (and supplier of weaponry to the Confederacy during the Civil War), thought that the most recent time period should be called the “Psychozoic era”.

He wrote: “The age of man…is characterised by the reign of the mind.” He believed that humankind had become the “chief agent of change” in the natural world and caused the extinction of various large species.

In 1922, Russian scientist Aleksei Pavlov first suggested that the current geological era should be called the “anthropogène”. The phrase gained traction in Soviet circles and was approved in 1963 as an equivalent to the Quaternary label — the period of time encompassing the most recent 2.6 million years, which is currently subdivided into the Pleistocene and Holocene — by the Interdepartmental Stratigraphic Committee of the USSR.

In the early 1920s, three scientists — Vladimir Vernadsky, Pierre Teilhard de Chardin and Edouard Le Roy — used the word “Noösphere” to describe how human thought was now capable of influencing the environment.

Outside of the USSR, however, the notion never really caught on. A paper published in Nature last year suggested that the idea of a period defined by humanity could have been politically convenient for the Soviet worldview:

‘A dangerous shift’

In 2000, Nobel-prize winning chemist Paul Crutzen and Great Lakes specialist Eugene F. Stoermer made reference to some of these scientists in a newsletter for the now defunct International Geosphere-Biosphere Programme. In this short article, they wrote:

It was this that revived the idea of the Anthropocene as a possible new geological time period and re-entered it into the scientific vernacular. Crutzen followed up the idea two years later with a paper in the journal Nature.

In this study, he distinguished his idea from the older notions of an anthropogenic age by suggesting that it started around 1784, at around the time when James Watt designed the steam engine — and when polar ice records show that concentrations of carbon dioxide and methane in the atmosphere started to rise.

Two academics — French philosopher Jacques Grinevald and Australian ethicist Clive Hamilton — argued that this new conception of the Anthropocene was a radical break from the past. Stoppani and his successors had conceived the era of humanity as a long process of incremental change to the landscape.

Now, the Anthropocene was presented as a dramatic rupture in the entire Earth system, write the authors. They said:

The Anthropocene

Infographic: The Anthropocene. By Rosamund Pearce for Carbon Brief.

The planet’s surface has changed enormously over the past two centuries, as humans have mined, cultivated, trawled, bleached and emitted their way forward with new technologies and higher populations.

New materials, such as plastic, concrete and aluminium, have spread across oceans and land. Nitrogen and phosphorus in soils have doubled over the past century as use of fertilisers has increased. Mining for copper, mercury and nickel has rapidly increased since the mid-20th century and nuclear testing has left its mark across the globe.

Then there’s climate change. Concentrations of CO2 have risen to more than 400 parts per million (ppm), from 285ppm at the start of the Industrial Revolution around the 1800s. Methane concentrations measured in Antarctic ice cores are higher than they have been for the past 800,000 years. Sea levels now exceed the past 115,000 years.

Not only have these changes been rapid, but they are still accelerating — and they will be evident in the geological record for hundreds of thousands of years to come.

All these impacts were listed in a paper that outlined the central findings of the working group set up to investigate whether the planet really had entered the age of the Anthropocene. This was published in early 2016 in the journal Science.

The group, formed in 2009, consists of 38 academics across a spectrum of disciplines, including geology, law and history. It was formed on the request of the Subcommission of Quaternary Stratigraphy, a group responsible for studying layers of rock over the last 2.6 million years.

This came on the back of a 2008 review by the Stratigraphy Commission of the Geological Society of London, which had made a case for incorporating the Anthropocene into the geological time scale.

But its remit stretches beyond simply looking for physical evidence in layers of rocks. Among its various activities are assessing the start date of the Anthropocene and the purpose of formally declaring a new epoch.

Utility and start date

The struggle to define the strata of time as they appear in the planet’s geology is not new. In the early 19th century, for instance, many considered the most recent layer of sediment to be a product of the Biblical Flood. It wasn’t until 1840 that glacial theory was accepted and termed the “Ice Age” by German poet Johann Wolfgang von Goethe.

But this case is particularly novel. “Not only would this represent the first instance of a new epoch having been witnessed firsthand by advanced human societies, it would be one stemming from the consequences of their own doing,” according to the Science paper from earlier this year.

There were initially a number of suggestions for the official start date of the Anthropocene. “To assign a more specific date to the onset of the ‘Anthropocene’ seems somewhat arbitrary, but we propose the latter part of the 18th century,” wrote Crutzen and Stoermer in their seminal article.

Other suggestions have included the advent of agriculture and deforestation which led to gradual increases of CO2 and methane thousands of years ago; the Columbian Exchange of species across continents following the voyage of Christopher Columbus in 1492; the beginning of the Industrial Revolution around 1800; and the mid-20th century “Great Acceleration” of population, industry and energy.

The working group also has the task of assessing why it actually matters. Jan Zalasiewicz, professor of paleobiology at the University of Leicester and convenor of the working group on the Anthropocene, tells Carbon Brief:

Another example of the practical applications of the Anthropocene concept arose soon after the working group had been established in 2009. Davor Vidas, director of the marine affairs and law of the sea programme at the Fridtjof Nansen Institute, got in touch to say that their efforts could be useful for his own sphere of work. He wrote in an email, published on the working group’s website:

Others are not so convinced of the term’s utility. Phil Gibbard, who, as set up the Anthropocene working group while he was chair of the Subcommission on Quaternary Stratigraphy, tells Carbon Brief:

Recommendation

Since the working group was established, there has been an explosion of interest in the topic.

In 2011, the Royal Society published a dedicated volume on the Anthropocene. The Geological Society of London published another one in 2014. A number of journals have been launched dedicated to the subject, including Elementa, Anthropocene and The Anthropocene Review. In 2019, the Smithsonian National Museum of Natural History is launching a new exhibition on “Deep Time”, which will feature a section on the Anthropocene.

In 2014, the word “Anthropocene” was accepted by the Oxford English Dictionary. Katherine Connor Martin, head of US dictionaries, tells Carbon Brief:

In the summer of 2016, after seven years of work, the working group came forward with its recommendation. At the 35th International Geological Congress in South Africa, it announced that the geological impact of humans was now so pronounced that the Anthropocene should take over from the Holocene, and that it should start from the Great Acceleration in the 1950s.

A lengthy process

While it might have made its recommendation, there are still various tasks to be done and organisations to be consulted before the working group’s recommendation can be made official. “There have been suggestions that our own work is proceeding on a geological timescale,” Zalasiewicz quipped in the working group’s 2014 newsletter.

Their next task is to find the “golden spike”. This is the colloquial term for what is formally known as the Global Boundary Stratotype Section and Point (GSSP) — a point in a specific rock that clearly shows the boundary between one age and another. Zalasiewicz says:

“We’ll suggest that we begin the process of looking around the world for a set of sections that could be sediments in lake beds, peat bogs, glaciers…where there are a set of signals to show the beginning of the Anthropocene. And then we’ll choose one of these to propose that ‘this is the reference point, this marks the beginning of the Anthropocene.’”

This process is expected to take two to three years. The outcome would form the basis of a formal proposal to their parent body, the Subcommission on Quaternary Stratigraphy, who will have to scrutinise the findings to date.

If they approve of the decision, then it is taken on to their parent body, the International Commission on Stratigraphy. With their approval, it can then be considered for ratification by the executive committee of the International Union of Geological Sciences.

Only at this point will the Anthropocene be formally declared as a new epoch. And despite the years of work, the outcome is not a foregone conclusion, Zalasiewicz tells Carbon Brief.

“One can’t predict whether our recommendations will be accepted. They are not always accepted for recommendations of ‘normal’ ancient strata, by any means.”

And there is resistance among geologists. Gibbard tells Carbon Brief that he has “sometimes” regretted setting up the group. He tells Carbon Brief:

“Are the conditions really that different? We’ve been influencing the natural environment since we started growing in numbers…I would argue the conditions which broadly characterise the Holocene still hold, so I would say we’re still in the Holocene.”

The problem has become something of a communications headache for geologists, he says, as the term has taken on a life of its own in recent years — something to which academics in the world of geology are not all that accustomed. But he stresses that the formal status of the Anthropocene does not necessarily have to be an either/or scenario. He says:

“If we’re going to define this term, I would see the Anthropocene being a division of the Holocene, not having equal status to Holocene. That’s where I would disagree with other workers.”

Yet whether or not geologists decide to formally inscribe a new epoch into their books, the influence of humans on the environment is unquestioned. Years of study have shown that the world is now a radically different place to when the Holocene began. It will continue to be moulded by humanity for millennia to come.